The present invention relates to a method of producing D-ribose by fermentation, and more particularly to a method of producing D-ribose using microorganisms belonging to the genus Bacillus modified by recombinant DNA technology so as to produce D-ribose efficiently.
D-ribose is contained in all organisms as a constituent component of ribonucleic acid, and ribitol, a reduced derivative thereof, is also contained as a constituent composition of vitamine B.sub.2 or ribitol teichonate constituting cell walls. This substance is therefore physiologically very important.
On the other hand, D-ribose has previously been used as a raw material for synthesis of vitamin B.sub.2, and has also recently been used as a raw material for synthesis of nucleic acid flavor enhancers. It is therefore industrially significant to prepare D-ribose at low cost and on a large scale.
The production methods of D-ribose hitherto known include the methods of extracting and isolating from natural products, the methods of synthesizing using furan, glucose, etc. as raw materials, and the fermentation methods using microorganisms (Japanese Patent Publication Nos. 47-7948/1972, 50-16878/1975, 51-7753/1976, 52-3/1977, 58-17591/1983 and 59-26276/1984).
On the other hand, enzymes such as gluconate permease involved in the permeation of gluconate in cells and gluconokinase producing 6-phosphogluconate from gluconate are present in Bacillus subtilis. These enzymes are coded for by a gene called gluconate operon. The gluconate operon (gnt operon) consists of four regions, gntR, gntK, gntP and gntZ [Y. Fujita et al., J. Biol. Chem., 261, 13744-13753 (1986)]. The expression of these enzymes is regulated by the expression regulating region (gntR) which is located adjacently upstream from the structural genes (gntK and gntP) coding for these enzymes [Y. Fujita et al., Pro. Natl. Acad. Sci. U.S.A., 84, 4524-4528 (1987)]. However, this document does not suggest the relationship to D-ribose producing ability at all.
All of the above-mentioned methods for producing D-ribose have disadvantages in that the production processes are complicated, in that the raw materials are expensive, or in that the yield is lowered by production of gluconate as a by-product. They are therefore not always satisfactory as industrial production methods for D-ribose at low cost. For this reason, a more advantageous method for producing D-ribose has been desired.